Natalie Portman is lugging a giant, heavy-looking sofa across the floor, to get away from what she mutters is the “brutal” heat of the sunlight beating down on the corner of a private beach club in Cannes. I feel I should help – I’m standing a few feet away, awaiting the signal to step forward – but the presence of one or two burly security staff nearby suggests I should stay damn well where I am. She’s dragging it while clad in the same fantastically flimsy Rodarte drapery and teetering high heels she wore for the film festival’s traditional photocall, a smidgeon of moxie underneath the carapace of glamour.

When the seating arrangements are aligned to her satisfaction, I finally get the nod and Portman greets me with radioactive smileyness, politely inquiring after my health. With the world’s press stacked up like aeroplanes taxiing on the runway, there’s not much time for small talk. We may not have seen much of Portman since Darren Aronofsky’s Black Swan – for which her portryal of the queen of all meltdowns won her the best actress Oscar – but she has since worked with the revered cinematic mystic Terrence Malick (playing opposite Christian Bale in Knight of Cups) and had the unnerving experience of the director Lynne Ramsay walk out on her most recent film, Jane Got a Gun. Now she is proudly escorting her directorial debut, A Tale of Love and Darkness, adapted from a memoir by Israeli novelist Amos Oz, to Cannes film festival.

Portman with Amos Oz. Photograph: Allen Berezovsky/Getty Images

“So many people have come up to me and said: ‘This is so brave of you’, and it never struck me as brave. The atmosphere in the US is so different than in Europe,” she says, alluding gently to the American (and Israeli) assumption that Europe is a hotbed of antisemitism. For Portman has taken on one of the most contentious subjects possible: the founding of the state of Israel in the late 1940s, refracted through the experience of Oz and his family. While Ryan Gosling’s self-indulgent Lost River got a royal roasting when it arrived at Cannes last year, the response to Portman’s film has been more in the vein of the frowning respect accorded to Angelina Jolie’s serious-minded debut, In the Land of Blood and Honey, about the mass rapes committed during the 1992-95 Bosnian war.

Born in Israel – she emigrated to the US with her family as a three-year-old – Portman remains unflappable in the face of what could become furious criticism; her film, after all, depicts the five key years of the Zionist project, between 1945 and 1950. Someone in her position, you would think, just doesn’t need the aggravation. But, she says, her confidence in Oz as an inspirational figure encouraged her to take the step: “I mean, he is the leader of the peace movement in Israel, the most peace-promoting, dialogue-inspiring person [and] the strongest supporter of the two-state solution and the strongest critic of the occupation of the West Bank, right from the beginning; he is still against it, and is an incredibly outspoken critic of it.”

It’s clear that Portman, with her record of support for a range of impeccably liberal causes (from poverty to animal rights to, um, vegan shoes), has the best of intentions; Israel’s rightward march in recent years seems as much to her distaste as anyone else’s. “You look at your country and it’s not what you want it to be,” she says. “It’s not what you wish it could be. But of course we have to strive for what could be, but also live with what exists, and what is, and be pragmatic.” She points to a scene early in the film, prominently positioned, where the young Amos is taken to an Arab neighbour’s party by his uncle; Amos becomes friendly with a little girl of about his age in the back garden, as they play together on a swing. He then, rather precociously, announces that “there is room for two peoples in this land”– but the apparent good-feeling is ruptured when, trying an overelaborate trick, he manages to break the swing and badly injure a toddler messing about nearby. The near-hysterical reaction to this incident is clearly meant to demonstrate the underlying tension between Palestine’s Jewish and Arab communities. It’s a scene that works well, with its tender symbolism, though is perhaps too clearly a message moment.

However, Portman points out that the film’s voiceover returns to brood on the incident as fighting breaks out after the UN vote to partition Palestine passes. “He was thinking about that girl; we are rejoicing, he is saying, and someone else is devastated right now. That is his empathetic nature, that I hope resonates throughout. That’s why it’s been surprising to me that people have interpreted it as anything but sympathetic.”

Portman’s central preoccupation, she says, is to “investigate the mythology” underlying the creation of Israel, something all too obviously obscured by the decades of rancour since. “The stories we tell is my main subject. What stories we tell to create our identity, what stories we tell to create our dreams. And then, when life doesn’t match those stories, how we deal with that. Where people are living in their dreams, and when that’s not the reality, you have to change your dreams.” Underneath the Hollywoodspeak, Portman is, I think, getting at the dream life of the Jewish state, which has persisted ever since Theodor Herzl published his 1896 pamphlet Der Judenstaat (The Jewish State).

All this is a long way from Portman’s beginning as a child actor, one of the few made properly good. Cast as an 11-year-old in the 1994 thriller Léon, her role opposite Jean Reno established her as a kind of forerunner of the now-ubiquitous manic pixie dream girl. By the end of the decade, though, she was adopting a graver persona as Queen Amidala in the three Star Wars prequels, which despite their limited potential for actual acting, performed as a kind of gateway to more grownup roles.

In 1999, she put her career on hold to study psychology at Harvard – famously telling the New York Post: “I don’t care if [college] ruins my career, I’d rather be smart than a movie star.” After graduating in 2003, she went to work in earnest, playing another manic pixie dream girl in Garden State, and then a stripper in the film adaptation of Patrick Marber’s play Closer. Her first proper blockbuster materialised with V for Vendetta, in which she played a girl caught up in an underground anarchist cell, while pitching for artsy status in films such as The Other Boleyn Girl (in which she played Anne Boleyn), Wong Kar-wai’s indulgent My Blueberry Nights and Wes Anderson’s celebrated short Hotel Chevalier. But these were hors d’oeuvres to the main course that was Black Swan: both an artistically credible film from one of America’s best directors, and a huge box office success, taking nearly $330m worldwide.

Black Swan also proved significant on a personal level: Portman began a relationship with the choreographer Benjamin Millepied, who was working on the film. The two have since had a son together, named Aleph (after the first letter of the Hebrew alphabet) and got married in 2012. Since Millepied secured the post of director of dance at the Paris Opera Ballet, the family has relocated to Paris. Her status now means she can combine bill-paying blockbusterdom – such as the two Thor movies, in which she plays astrophysicist Jane Foster – with far more recondite material – Malick’s Knight of Cups, a dream-fantasy set in Los Angeles, being a prime recent example.

Despite her considerable experience, Portman has found herself grappling with same gender issues that have electrified the current generation of women filmmakers. She was, for example, painfully reluctant to direct herself. “I was afraid of appearing vain. I remember as a kid reading about Barbra Streisand directing herself in movies, and people would write that they were just vanity projects. But then I realised that was something they would never say about men directing themselves.” She also says she was inspired by seeing “women, younger women than I am, Lena Dunham, Greta Gerwig, Brit Marling, just creating their own things” and that she “teared up” at seeing Dunham’s triple credit – writing, directing, and acting – on her debut film, Tiny Furniture. “It’s a very female thing of being afraid to say: ‘I’m the boss, and this is how I want it.’ ”

Be that as it may, can Portman survive the buffeting she will likely receive when A Tale of Love and Darkness makes its way out to the wider world? For her, the film clearly emerges from a personal space, from her cultural identification with her Israeli childhood. But there will no doubt be large numbers of people who don’t want to know. “Obviously, I want the audience to take away from it what they will. It resonates with my own family’s histories and mythologies and the kinds of things I grew up hearing. I wanted to find out if these stories really happened.”